This invention relates to a novel process for producing polyester resin using regenerated polyester which has been recovered from waste materials such as disused PET (polyethylene terephthalate) bottles, and also to paint compositions containing the polyester resin prepared by said process.
Disposal of wastes has been recently causing serious problems, and xe2x80x9c3R""sxe2x80x9d (Recycle, Reduce and Reuse) are recommended. In particular, recycling of disused PET bottles is being promoted, led by the Council for PET Bottle Recycling in Japan Aided by the complete enactment of Containers and Packagings Recycling Act in April, 2000, the recovery ratio of disused PET bottles has been steadily increasing. Under the circumstances, it is essential to enlarge utility of the recovered and regenerated polyester (recycled polyester).
For example, U.S. Pat. No. 5,252,615, EP-A-558,905 and EP-A-558,906 disclose a process for producing intended polyester resin, which comprises subjecting a polyhydric alcohol component and regenerated PET to a depolymerization reaction in the presence of a catalyst to reduce the molecular weight of the PET, and adding a polybasic acid component to the system to carry out a polycondensation reaction. Those publications also teach that the resulting polyester resin is useful for both water-based and non-water-based coating compositions. However, the same process requires many hours for the depolymerization reaction of polyhydric alcohol component with regenerated PET, and the production costs are high compared to conventional processes which do not use regenerated polyester.
The Official Gazette of Hei 11 (1999)-228733A-JP discloses a process for synthesizing polyester resin through ester-interchange reaction of recycled polyester such as regenerated PET with a polyester oligomer having a molecular weight not higher than 5,000. However, this process is subject to a number of problems that it requires an extra step of advance synthesis of said polyester oligomer; its depolymerization step requires many hours because sufficient depolymerization of recycled polyester is difficult due to insufficient amount of alcohol component in the depolymerization system and also because it is a reaction between high molecular weight compounds; and the filtration residue is apt to form in large quantities.
Furthermore, Hei 8 (1996)-253596A-JP discloses a production process of binding resin for toners which comprises the two steps of adding recycled polyester such as regenerated PET to the reaction system to carry out the polymerization while depolymerizing the recycled polyester in the presence of alcohol and if necessary, water; and then of adding an acid component to carry out addition reaction and increasing the molecular weight of the product. According to this process, the first step is a reaction in the system in which a large excess (at least approximately twice) of hydroxyl groups to carboxyl groups are present, and depolymerization of recycled polyester predominantly takes place. Hence the polyester formed in the first step has a low molecular weight, and in the second step an acid component is blended to carry out the addition and polymerization reaction. Thus, the process does not enable effective one-step synthesis of high molecular weight polyester resin. The process attempts to synthesize relatively low molecular weight polyester in the first step and to increase its molecular weight in the second step by adding an acid component. Whereas, the process uses, as the acid component to be added in the second step, tri- or higher functional acid in large quantities to form branched polymers, which involve a problem that they are apt to be gentled as their molecular weight increases.
The main object of the present invention is to provide a process for producing within a short time a high molecular weight polyester resin free of any problem in respect of physical properties, which is transparent and substantially free of formation of foreign matters or filtration residues, from the polyester resin recovered from waste materials and regenerated.
We have engaged in concentrative studies with the view to accomplish the above object, and now discovered that the object can be met by concurrently reacting the polyester resin made chiefly from terephthalic acid, which has been recovered from waste materials and regenerated, with an alcoholic component and an acid component. The present invention has thus been completed.
Accordingly, therefore, the present invention provides a process for producing a polyester resin having a resin acid value not higher than 120 mg KOH/g, hydroxyl value not higher than 120 mg KOH/g and a number-average molecular weight within a range of 2,000-30,000, the process being characterized by concurrently reacting a polyester whose chief starting material is terephthalic acid and which has been recovered from waste materials and regenerated, a polyhydric alcohol component and polybasic acid component, at such ratios that the regenerated polyester occupies 10-80% by weight, based on the total weight of said regenerated polyester, polyhydric alcohol component and polybasic acid component.
The invention furthermore provides paint compositions which contain the polyester resin produced by the above-described production process.
Hereinafter the invention is explained in further details. Those polyester resins made chiefly from terephthalic acid, which have been recovered from waste materials and regenerated, and which are used in the process of this invention (hereafter the polyester resins may be abbreviated as xe2x80x9cregenerated PESxe2x80x9d) include polyethylene terephthalate (e.g., PET bottles) which are recovered for recycling of sources, industrial waste polyethylene terephthalate, and polyester resins regenerated from the wastes occurring in the course of production of polyester products (film, fibers, etc.) made chiefly from terephthalic acid. In particular, recycled polyethylene terephthalate and recycled polybutylene terephthalate are suitable. The regenerated PES is normally used in the form of chips or crushed pieces.
According to the process of the present invention, such regenerated PES, polyhydric alcohol component and polybasic acid component are concurrently reacted, if necessary in the presence of a depolymerization catalyst.
As said polyhydric alcohol component, those that are normally used as alcohol component for constituting polyester resins can be similarly used, examples of which including dihydric alcohols such as ethylene glycol, diethylene glycol triethylene glycol propylene glycol, 1,3-propanediol 2-methyl-1,3-propanediol 2,2-diethyl-1,3-propanediol, 2-butyl-2-diethyl-1,3-propanediol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and 1,4-dimethylolcyclohexane; trihydric alcohols such as trimethylolpropane, trimethylolethane and glycerine; and tetra- and higher hydric alcohols such as diglycerine, triglycerine, pentaerythritol, dipentaerythritol and sorbitol. Of those, glycerine, trimethylolpropane, ethylene glycol, neopentyl glycol and 1,4-dimethylolcyclohexane are preferred in view of their depolymerizing ability and solubility.
As the polybasic acid component, any of those normally used as the acid component forming polyester resin can similarly be used, examples of which including dibasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, naphthalenedicarboxylic acid, 4,4xe2x80x2-biphenyldicarboxylic acid, diphenylmethane-4,4xe2x80x2-dicarboxylic acid, succinic acid, fumaric acid, adipic acid, sebacic acid and maleic anhydride; tri- and higher polybasic acids such as trimellitic anhydride, pyromellitic anhydride, trimesic acid and methylcyclohexene-tri-carboxylic acid; and C1-C6 alkyl esters of those dibasic acids and tri- and higher polybasic acids. Of those, dibasic acids and their C1-C6 alkyl esters are preferred.
According to the process of the present invention, above-described regenerated PES, polyhydric alcohol component and polybasic acid component are combined and reacted simultaneously. In that occasion, the three components are used at such quantitative ratios that the amount of the regenerated PES is within the range of, based on the total weight of said three components, 10-80%, preferably 20-70%, inter alia, 30-60% by weight, and that the polyester resin obtained according to the process of the invention has a resin acid value not more than 120 mg KOH/g, preferably within a range of 1-80 mg KOH/g, and the hydroxyl value, not more than 120 mg KOH/g, preferably 1-80 mg KOH/g. In particular, it is desirable to use the polybasic acid component and polyhydric alcohol component at such ratios that the equivalent ratio of COOH/OH be within the range of 0.75-1.33, preferably 0.80-1.25.
According to the process of the invention, depolymerization of the regenerated PES and the esterification simultaneously take place to form polyester resin. The term, xe2x80x9cesterification reactionxe2x80x9d as used herein includes not only ordinary esterification reaction but also ester interchange reaction. While the depolymerization progresses in the absence of catalyst at reaction temperatures higher than the melting point of regenerated PES (at about 240xc2x0 C. and above), use of a depolymerization catalyst is preferred to carry out the depolymerization at temperatures lower than the melting point or to perform it more effectively.
Examples of depolymerization catalyst include monobutyltin hydroxide, dibutyltin oxide, monobutyltin-2-ethyl hexanoate, dibutyltin dilaurate, stannous oxide, tin acetate, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, litharge, antimony trioxide, tetrabutyl titanate and tetraisopropyl titanate. The use rate of the depolymerization catalyst is not critical, while generally it is preferred to be not more than 10 parts, in particular, within a range of 0.001-5 parts by weight, per 100 parts by weight of the total sum of the regenerated PES, polyhydric alcohol and polybasic acid. Normally the depolymerization catalyst can also serve as esterification (polymerization) catalyst.
The process of the present invention comprises the reaction of above-described regenerated PES, polyhydric alcohol component and polybasic acid component all in one system, in the optional presence of a depolymerization catalyst, in which the depolymerization reaction of the regenerated PES and the esterification reaction (including ester-interchange reaction) among the regenerated PES, polyhydric alcohol component and polybasic acid component progress concurrently to produce the intended polyester resin. The reaction conditions are not critical so long as said depolymerization reaction and the esterification reaction progress simultaneously. Whereas, generally the intended polyester resin can be produced by mixing the three components and reacting them under stirring at about 160xe2x80x94about 270xc2x0 C., preferably at about 180xe2x80x94about 250xc2x0 C., for about 2-10 hours. When the polyhydric alcohol component used in the reaction is in solid form, it is preferably heated in advance and melted. After termination of the reaction, so synthesized polyester resin is normally cooled and isolated from the reaction mixture as it is, or for improving its filterability and handling property, may be diluted with an organic solvent and recovered. The kind of useful organic solvent used in that occasion is subject to no limitation so long as it can dissolve the polyester resin.
According to the above-described process of the present invention, an advantage of drastic reduction in reaction time is attained, by the concurrent reaction of regenerated PES, a polyhydric alcohol component and polybasic acid component.
Thus produced polyester resin has a resin acid value not higher than 120 mg KOH/g, preferably 1-80 mg KOH/g; a hydroxyl value not higher than 120 mg KOH/g, preferably 1-80 mg KOH/g; and a number-average molecular weight within a range of 2,000-30,000, preferably 2,500-20,000. In particular, the polyester resin having a resin acid value of 2-80 mg KOH/g, a hydroxyl value of 2-80 mg KOH/g and a number-average molecular weight of 2,500-10,000 is preferred. Furthermore, the chloroform-insoluble component of the produced polyester resin is preferably not more than 1.0%, i.e., that the regenerated PES has been sufficiently decomposed and the formed polyester has a uniform composition, because such a polyester resin gives favorable appearance to painted film when it is incorporated in paint.
Those polyester resins produced according to the process of the present invention are useful as the resin binder in paint compositions, and when they have a glass transition temperature not lower than about 30xc2x0 C., they are also useful as the resin binder for powder coating compositions.
When the polyester resins obtained according to the process of the present invention contain hydroxyl groups, they can be conveniently used as resins for thermosetting paint, in combination with a curing agent which is reactive with hydroxyl groups, e.g., an amino resin such as melamine resin, polyisocyanate compound, epoxy compound and the like. On the other hand, when the polyester resins contain carboxyl groups, they can be conveniently used as resins for thermosetting paint, in combination with a curing agent which is reactive with carboxyl groups, such as an epoxy compound.
For formulating a paint composition using a polyester resin obtained according to the process of the invention, known paint additives such as organic pigment, inorganic pigment, filler, curing catalyst, surface control agent (anti-cissing agent), flow-and-leveling agent, ultraviolet absorber, ultraviolet stabilizer, organic solvent and the like may be added if necessary, besides the polyester resin and a curing agent as above-described. When the polyester resin has a glass transition temperature not lower than 30xc2x0 C., it can be conveniently used as a resin for powder coating composition. For preparing such a powder coating composition, practices known per se for formulating powder coating compositions can be followed, e.g., by combining the polyester resin, a curing agent and other paint additives if necessary, dry-blending them in a mixer, heat-melting, kneading, cooling, coarse crushing, finely pulverizing and classifying, a powder coating composition can be prepared.
The paint composition in which the polyester resin obtained by the process of the present invention is used can form cured baked film upon being applied onto an object matter and baked. The baking conditions are not critical and can be suitably chosen so long as the applied paint can be cured thereunder. Normally, when baking temperature of about 120xe2x80x94about 210xc2x0 C. is used, the baking time is around 5-30 minutes, and where the baking temperature conditions under which the maximum temperature of the object matter reaches about 180xe2x80x94about 250xc2x0 C., preferred baking time is less than 5 minutes.
Hereinafter the invention is more specifically explained with reference to Examples in which parts and percentages are by weight.